Sb-containing catalysts by Sb-oxide impregnation

ABSTRACT

Antimony-based oxide complex catalysts are improved by adding to these catalysts an antimony-containing compound such as Sb 2  O 3 .

BACKGROUND OF THE INVENTION

The present invention relates to a technique for improving the catalyticproperties of various antimony-containing oxide complex oxidationcatalysts.

Oxidation catalysts in which antimony forms an integral part of the basecatalyst system have been used for various types of oxidation reactions,e.g. oxidation of olefins to produce aldehydes and acids, ammoxidationof olefins to produce unsaturated nitriles and oxydehydrogenation ofolefins to produce diolefins such as isoprene. For example, note U.S.Pat. No. 3,431,292, which discloses various uranium antimonate catalystsuseful in various oxidation reactions, U.S. Pat. No. 3,338,952, whichdiscloses iron antimonate catalysts useful in various oxidationreactions, and U.S. Pat. No. 3,296,957, which discloses various tinantimonate catalysts useful in various oxidation reactions. Thedisclosures of all these patents are incorporated herein by reference.

While catalysts described in the prior art are capable of providing goodyields of the desired end products, it is always beneficial to improvethe performance of catalysts so that they can provide even betteryields.

Accordingly, it is an object of the present invention to provide atechnique for forming new antimony-containing oxide complex oxidationcatalysts which yield catalysts having improved catalytic properties.

In addition, it is a further object of the invention to provide a noveltechnique for processing used antimony-containing oxide complexcatalysts to rejuvenate the catalytic properties thereof.

SUMMARY OF THE INVENTION

These and other objects are accomplished by the present invention whichis based on the discovery that the catalytic properties of variousantimony-containing oxide complex oxidation catalysts can be improved byadding to these catalysts an antimony compound.

Thus, the present invention provides a process for improving thecatalytic performance of an antimony-containing oxide complex catalystcomprising adding to the catalyst an antimony-containing compound in anamount such that the amount of antimony added to the catalyst is 0.1% to25% based on the antimony in the catalyst.

DETAILED DESCRIPTION Catalysts

The present invention can be practiced on any antimony-containing oxidecomplex catalyst, whether new or used. The invention is preferablypracticed on "antimony-based" catalysts, i.e. catalysts which contain atleast about 20 atom percent antimony based on the total atoms in thecatalyst, excluding oxygen and, of course, excluding any support whichmight be used. Such catalysts are well known and described inter alia inthe patents mentioned above.

For convenience, these catalysts can be described as oxide complexes ofthe formula:

    A.sub.a B.sub.b C.sub.c M.sub.d Sb.sub.e O.sub.x

wherein

M is U, Fe, Mn, Ce, Th, Sn, Ti or mixtures thereof, preferably U, Fe, Snor mixtures thereof;

A is Mo, W or mixtures thereof;

B is V, Te, Cr, Cu, Bi or mixtures thereof; and

C is Ni, Co, alkali metal, alkaline earth metal or mixtures thereof; and

wherein

0≦a≦10;

0≦b≦10;

0≦c≦10;

0.1≦c≦10;

5≦e≦100; and

x is a number sufficient to satisfy the valence requirements of theother elements present.

Preferably

0≦a≦5;

0≦b≦5;

0≦c≦5; and

0.1≦d≦10.

As previously indicated, preferred catalysts processed by the presentinvention are those whose antimony content is at least 20 atom percentbased on the total number of atoms in the oxide complex excludingoxygen. Most preferably, the amount of antimony in the oxide complex isat least 35%, even more preferably 50% based on the number of atoms inthe complex excluding oxygen.

A preferred group of catalysts are those in which M is U, Fe, Sn ormixtures thereof, and further wherein c/d equals 1/3 to 1/6, preferably1/4 to 1/5.

As indicated above, the oxide complex catalysts used in the presentinvention can be supported on a support, as is conventional. Any knownsupport, such as silica, alumina, Alundum, graphite, titania, zirconiaand the like, can be used. It will be understood that the variousproportions, ratios and percentages given in this specification are madewith respect to the oxide complex, the support being excluded.

Antimony-Containing Compound

In accordance with the present invention, antimony-containing oxidecomplex catalysts as described above are impregnated with (i.e. mixedwith) an antimony-containing compound. Usually, the antimony compoundwill be an oxide of antimony such as Sb₂ O₃, Sb₂ O₄ and Sb₂ O₅. Otherantimony-containing compounds, however, can be used. For example,antimony halides such as SbCl₂, SbCl₃, SbCl₅ and SbF₅ can be used aswell as various antimony-containg organo-metallic compounds such as Ph₃Sb, Et₄ SbCl, Me₄ SbI (wherein Ph is phenyl, Et is ethyl and Me ismethyl). In accordance with one embodiment of the invention, variousmetal antimonates can be used. In this situation, it is desirable thatthe metal in the metal antimonate also be a component of theantimony-based oxide complex being treated. For example, if theantimony-based catalyst being processed is a complex iron antimonate, itis appropriate to use iron antimonate as the antimony compound. Examplesof various metal antimonates which can be employed are VSbO₄, NiSb₂ O₆,CoSb₂ O₆, MnSbO₄, Fe₂ Sb₂ O₇, FeSb₂ O₆, USb₃ O₁₀ and the like.

It is also possible to use antimony compounds containing metals otherthan those in the oxide complex. It is desirable, however, to avoidusing compounds containing elements which will poison the catalyst.

Means Of Impregnation

The antimony-containing compound can be added to the antimony-containingoxide complex catalyst processed in accordance with the presentinvention in any manner. If the antimony-containing compound is aliquid, then it is easiest simply to use that compound as is. Normally,however, the antimony-containing compound will be a solid, and in thissituation the compound can easily be employed by forming an aqueousslurry of a fine powder of the compound. In accordance with thisprocedure, it is desirable to form a powder of the compound having aparticle size of below 40 microns, preferably below 20 microns. Thispowder can then be easily formed into an aqueous slurry having a solidscontent preferably below 50, more preferably below 20 weight percent.Such a slurry can then be easily applied to the antimony-containingoxide complex to impregnate the same with the antimony-containingcompound.

Still another technique for adding the antimony compound is to dissolveor disperse the antimony compound in an organic medium and impregnatethe catalyst with this solution and/or dispersion. Organic media such asorganic acids and organic nitriles have been found useful for thispurpose. Also useful are aqueous ammonia and anhydrous ammonia. Also,the antimony compound if in powder form can be simply charged into anoperating reactor containing an antimony-containing catalyst.

In a preferred embodiment of the invention, the impregnant is applied bymeans of an aqueous nitric acid solution. The presence of nitric acid inthe aqueous slurry is beneficial because it causes or promotes oxidationof Sb⁺³ to higher valence states. Since antimony-based oxide complexcatalysts seem to exhibit better catalytic properties when antimony isin a higher valence state, it is desirable in accordance with thepresent invention that the antimony added to the oxidation catalyst alsobe in higher valence states. If a nitric acid aqueous slurry is used,the aqueous slurry should preferably be about 100 to 1, more preferably50 to 1 weight percent in nitric acid.

Amount of Antimony Compound Added

The amount of antimony-containing compound impregnant deposited on theoxide complex catalyst can vary widely. Normally, the amount ofimpregnation will be such that the amount of antimony on an atomic basisadded to the oxidation catalyst is between about 0.1 and 25% based onthe number of atoms in the oxide complex. While less than 0.1% antimonycan be added, the improvement realized is minimal, while greater than25% impregnation also yields little if any improvement over a 25%impregnation. Preferably, the amount of impregnation is 0.5 to 20%, morepreferably 2 to 10%, most preferably about 3 to 5%.

Post-Impregnation Processing

After the antimony-based oxidation catalyst is impregnated in accordancewith the present invention, it is processed in the same way thatcatalyst precursors derived from aqueous slurries, i.e. the solidsrecovered from an aqueous slurry during catalyst preparation, areprocessed to form antimony-based oxidation catalysts. Thus, theimpregnated oxidation catalyst is normally dried and then heated inelevated temperature in the presence of an oxygen-containing gas,usually air, for an extended period of time. In other words, thecatalyst is subjected to conventional calcination. In carrying out thiscalcination, the catalyst is normally heated in air to temperaturesranging from 200° C. to 1,200° C. for periods of from 0.5 to 50 hours.Normally, the catalyst is heated to temperatures of 550° C. to 950° C.for periods of 0.2 to 3 hours. Of course, if the catalyst to beprocessed contains nitrates, as for example if a nitric acid aqueousslurry is employed for impregnation, then the catalyst can be subjectedto a staged calcination as is conventional. As well known, in such acalcination procedure, the catalyst is first heated at a relatively lowtemperature, e.g. about 250° C. to 450° C., to decompose the nitratestherein and drive off the decomposition products and thereafter heatedat a higher temperature to set the final catalytic structure of thecatalyst.

Catalyst Uses

The impregnated catalyst produced in accordance with the presentinvention can be used in the same way and for the same purposes as knownantimony-based oxidation catalysts. For example, they can be ideallyused in the ammoxidation of propylene or isobutylene to acrylonitrileand methacrylonitrile respectively, the oxidation of olefins such aspropylene and isobutylene to produce the corresponding unsaturatedaldehydes and acids, and the oxydehydrogenation of various compoundssuch as isoamylene to produce the corresponding di-unsaturatedcompounds. The types of reactions these catalysts can be employed in andthe way in which they can be used are exemplified in commonly assignedapplication Ser. No. 095,886, the disclosure of which is incorporatedherein by reference.

WORKING EXAMPLES

In order to more thoroughly describe the present invention, thefollowing working examples are presented. In these examples, variousantimony-based oxidation catalysts were prepared. In addition, each ofthese catalysts was impregnated with Sb₂ O₃ in accordance with thefollowing procedure.

0.8 gms. of Sb₂ O₃ was added to 50 ml. concentrated nitric acid andheated with stirring at 80° C. for approximately 2.0 hours. The slurrywas then filtered and washed several times with distilled water. Thefiltrate so obtained was added to an aqueous slurry of 20 gms. of theindicated catalyst in 200 ml. of distilled water. The mixture wasstirred and heated at 90° C. for 3 hours and then allowed to evaporateslowly to dryness. The residue was then heat treated at 290° C. for 3hours to cause denitrification and then at 450° C. for 3 hours to formfinal calcination. The catalyst was then ground and screened and theportion of the catalyst having a particle size of from 20 to 35 mesh wasrecovered as the objective catalyst.

Each of the catalysts so produced as well as the correspondingunimpregnated antimony-based oxide catalyst were tested in theammoxidation of propylene to produce acrylonitrile. In each test, 5 cc.of catalyst was charged into a 6.5 cc. micro-reactor and contacted witha feed containing 1 propylene/1.2 NH₃ /10.5 air/4 H₂ O at 445° C.±15° C.at a 3 second contact time. The gross reaction product was recovered andanalyzed for acrylonitrile yields. The results obtained are set forth inthe following Table I.

                                      TABLE I                                     __________________________________________________________________________                          Unreacted                                                                           Acrylonitrile                                     Example                                                                            Catalyst Composition                                                                           Propylene                                                                           Yields*                                                                           Select.**                                     __________________________________________________________________________    Comp. A                                                                            Cr.sub.12 Sb.sub.14 Fe.sub.1 Mo.sub.1 O.sub.x + SiO.sub.2                                      28.7  18.4                                                                              25.9                                          1    Comp. A + Sb.sub.2 O.sub.3 Impreg.                                                             39.4  30.3                                                                              49.9                                          Comp. B                                                                            Fe.sub.12 Sb.sub.25 Cu.sub.3 Te.sub.2 W.sub.0.2 Mo.sub.1 O.sub.x +            SiO.sub.2        4.7   76.4                                                                              80.1                                          2    Comp. B + Sb.sub.2 O.sub.3 Impreg.                                                             1.3   80.5                                                                              81.5                                          Comp. C                                                                            Fe.sub.12 Sb.sub.25 Cu.sub.3 Bi.sub.2 W.sub.0.2 Mo.sub.1 O.sub.x +            SiO.sub.2        1.3   75.4                                                                              76.4                                          3    Comp. C + Sb.sub.2 O.sub.3 Impreg.                                                             0.7   78.9                                                                              79.5                                          __________________________________________________________________________     *Moles acrylonitrile produced divided by Moles propylene fed                  **Moles acrylonitrile produced divided by Moles propylene reacted        

From the foregoing, it can be seen that catalysts impregnated with anantimony-containing compound provide acrylonitrile yields superior tothose obtained from the antimony-based oxide complex catalyst itself.Thus, the present invention provides a simple and straightforward methodfor improving the catalytic properties of various antimony-containingcatalysts.

Although only a few embodiments of the present invention have beendescribed above, many modifications can be made without departing fromthe spirit and scope of the invention. All such modifications areintended to be included within the scope of the present invention, whichis to be limited only by the following claims.

We claim:
 1. A process for improving the catalytic performance of a usedantimony-containing oxide complex catalyst comprising adding to saidcatalyst an antimony-containing compound in an amount such that theamount of antimony added to said catalyst is 0.1 to 25% based on theantimony in said catalyst.
 2. The process of claim 1 wherein 25% to 10%antimony is added to said catalyst.
 3. The process of claim 2 whereinsaid antimony-containing compound is an oxide of antimony.
 4. Theprocess of claim 3 wherein said antimony-containing compound is appliedby means of an aqueous nitric acid slurry.
 5. The process of claim 4wherein said oxide complex catalyst is defined by the formula:

    A.sub.a B.sub.b C.sub.c M.sub.d Sb.sub.e O.sub.x

wherein M is U, Fe, Mn, Ce, Th, Sn, Ti or mixtures thereof; A is Mo, Wor mixtures thereof; B is V, Te, Cr, Cu, Bi or mixtures thereof; and Ois Ni, Co, alkali metal, alkaline earth Metal or mixtures thereof;andwherein 0≦a≦10; 0≦b≦10; 0≦c≦10; 0.1≦d≦10; 5≦e≦100; and x is a numbersufficient to satisfy the valence requirements of the other elementspresent.
 6. The process of claim 5 wherein M is Fe, Sn or mixturesthereof, and further wherein c/d is 1/3 to 1/6.
 7. The process of claim5 wherein 0≦a≦5, 0≦b≦5 and 0≦c≦5.
 8. The process of claim 1 wherein saidcatalyst is defined by the formula:

    A.sub.a B.sub.b C.sub.c M.sub.d Sb.sub.e O.sub.x

wherein M is U, Fe, Mn, Ce, Th, Sn, Ti or mixtures thereof; A is Mo, Wor mixtures thereof; B is V, Te, Cr, Cu, Bi or mixtures thereof; and Cis Ni, Co, alkali metal, alkaline earth metal or mixtures thereof;andwherein 0≦a≦10; 0≦b≦10; 0≦c≦10; 0.1≦d≦10; 5≦e≦100; and x is a numbersufficient to satisfy the valence requirements of the other elementspresent.
 9. The process of claim 1 further comprising heating saidantimony-containing oxide complex catalyst after impregnation with saidantimony-containing compound in air at 200° to 1200° C. for 0.5 to 50hours.
 10. An improved antimony-based oxidation catalyst comprising aused antimony-based oxide complex defined by the formula:

    A.sub.a B.sub.b C.sub.c M.sub.d Sb.sub.e O.sub.x

wherein M is U, Fe, Mn, Ce, Th, Sn, Ti or mixtures thereof; A is Mo, Wor mixtures thereof; B is V, Te, Cr, Cu, Bi or mixtures thereof; and Cis Ni, Co, alkali metal, alkaline earth metal or mixtures thereof;andwherein 0≦a≦10; 0≦b≦10; ≦ c≦10; 0.1≦d≦10; 5≦e≦100; and x is a numbersufficient to satisfy the valence requirements of the other elementspresent.impregnated with 0.1 to 25% of an antimony-containing compoundimpregnant, the percents being based on the atoms of antimony in theimpregnant and the atoms of antimony in said oxide complex, saidimproved antimony-based oxidation catalyst capable of producingacrylonitrile in the ammoxidation of propylene in greater yields thansaid used oxide complex.
 11. The improved catalysts of claim 9 whereinsaid impregnate is an oxide of antimony.
 12. A process for improving thecatalytic performance of an antimony-containing oxide complex catalystdefined by the formula:

    A.sub.a B.sub.b C.sub.c M.sub.d Sb.sub.e O.sub.x

wherein M is Fe, Mn, Ce, Th, Sn, Ti or mixtures thereof; A is Mo, W ormixtures thereof; B is V, Te, Cr, Cu, Bi or mixtures thereof; and C isNi, Co, alkali metal, alkaline earth metal or mixtures thereof;andwherein 0≦a≦10; 0≦b≦10; 0≦c≦10; 0.1≦d≦10; 5≦e≦100; and x is a numbersufficient to satisfy the valence requirements of the other elementspresent,said process comprising adding to said catalyst anantimony-containing compound in an amount such that the amount ofantimony added to said catalyst is 0.1 to 25% based on the antimony insaid catalyst.
 13. The process of claim 12 wherein M is Sn, Fe ormixtures thereof.
 14. The process of claim 13 wherein saidantimony-containing oxide complex catalyst is a used catalyst.
 15. Theproduct of the process of claim
 14. 16. The product of the process ofclaim
 13. 17. The product of the process of claim 12.